Air washers are a conventional piece of apparatus utilized in humidity control in industrial and commercial systems. A conventional air washer includes one or more banks of nozzles placed in an air stream to be treated, which nozzles receive chilled water under pressure from a source and atomize the water into a spray that is introduced into the air stream. In normal or humidifying operations, moisture from the spray is picked up by the air stream as a result of evaporative cooling.
During summertime operations, the same air washer can be used as a dehumidifying apparatus. In such situations, the return air is generally higher in humidity than desired, and therefore if the spray water is maintained at a cooler temperature than the air stream, moisture from the air stream will condense on the tiny water droplets, which are subsequently removed from the air stream, resulting in less moisture in the air stream provided back to the work area.
When the air washer is being utilized as a dehumidifying device, sometimes it is necessary to remove more moisture than at other times. When the amount of moisture to be removed from the return air is small (minimum spray condition), a problem occurs because while the number of water droplets must be reduced, the water pressure must still be high enough to maintain atomization. Therefore, in one approach, by merely reducing the water pressure through throttling valves, complete atomization may not occur. In such a case, the opposite result, i.e. evaporative cooling will occur and the return air stream will actually pick up moisture.
In a first attempt to overcome this problem, it was attempted to shut off certain lower ones of the spray nozzles leaving only the upper nozzles active, even though the pressure was maintained on the upper nozzles to promote atomization. While moisture will initially condense in the upper regions of the air stream, by the time the droplets fall to the collecting tank below, evaporative cooling will again occur, thus adding moisture to the return air stream.
In the present approach, which has been found to be effective, the water supply is divided into one branch which is directed to an upper header, thereby feeding water to upper ones of the nozzles in a bank. The other branch of water is directed to a lower header that feeds the lower nozzles. The branch pipe to the upper header is provided with a throttling valve upstream of the upper header, so that the water pressure may be reduced thereto or even shut off completely. Even though the upper nozzles may be shut off, atomization still occurs through the lower nozzles. The droplets emitted by the lower nozzles will condense sufficient moisture from the air stream to achieve the minimum dehumidification necessary.
In a preferred approach, the throttling valve to the upper header is activated responsive to a thermostat in the work area being controlled. When the thermostat indicates that the temperature is decreasing past prescribed limits, the throttling valve is activated to begin reducing the supply of water to the upper sprays until the temperature rises back above the prescribed limit. It may even be necessary to shut off the upper sprays completely to maintain temperature above the prescribed lower limit. However, should this occur, the supply of water to the lower nozzles is maintained at sufficient pressure to effect atomizations and achieve the desired dehumidification result.
It has also been found in a preferred embodiment that the nozzles being supplied by the lower header which are not shut off or throttled should make up a minor portion of the total number of nozzles (10-15%).
It is therefore an object of the present invention to provide an improved apparatus and method for operating an air washer as a dehumidification device even during times of minimum spray conditions and prevent humidification during such times as a result of evaporative cooling.
It is a further object of the present invention to provide an apparatus and method of the type described in which the desired result is achieved by throttling or shutting off the water supply to a major portion of the nozzles of the air washers while maintaining the water supply at normal pressures to a minor portion of nozzles that are positioned in the lower regions of the air stream.